In vivo 31-P nuclear magnetic resonance (NMR) techniques have been used to evaluate the effects of several toxic substances on tissue metabolism, with particular emphasis on the potential significance of changes in the levels of non-cyclic phosphodiesters. In mammalian systems, the phosphodiesters glycerophosphoryl choline (GPC) and glycerophosphoryl ethanolamine (GPE) are readily observed in many tissues and hence are present at near millimolar levels. Although most generally postulated to be lipid catabolites, it is difficult to reconcile this lack of function with the high tissue levels observed. Further, the presence of analogous phosphodiesters such as serine ethanolamine phosphodiester (SEP) which is found in the chicken, and threonine ethanolamine phosphodiester (TEP) which we have found to be the major phosphorus-containing metabolite in fish lens, also suggests functions beyond that of lipid breakdown product. In the most recent studies it appears that TEP might be present in some mammalian tumors. To investigate this, authentic TEP has been isolated from fish lens and will be compared to the resonance in tumor extracts. Since fish tissue contains the novel lipid phosphatidyl threonine, studies arrived at characterizing the corresponding pH and 31P resonances are in progress. Finally to expand the range of toxins investigated, the neurotoxin triphenylphosphite, has been studied. In particular, its influence on tissue at the site of injection has been characterized by surface coil analysis. It was possible not only to examine the intercellular phosphates but also to follow the course of absorption of the toxin.